What are the importance of letters in the novel of Clarissa by Samuel Richardson? What are their functions?

Samuel Richardson’s nine-volume novel Clarissa Harlowe or the History of a Young Lady is what is known as an epistolary novel, meaning it is told through fictitious journal or diary entries and through correspondence between characters, as opposed to a straight-forward narrative told in the first or third person. That Richardson’s novel, the longest ever written, is categorized as epistolary is suggested in the novel’s first sentence, specifically, in Richardson’s preface:

“The following History is given in a series of letters, written Principally in a double yet separate correspondence;”

As the attached link to volume one of the novel demonstrates, the entire text is a long (very long) series of letters between characters. This format would be used by many authors throughout the ages, with Bram Stoker’s Dracula and Mary Shelley’s Frankenstein being two of the more prominent examples. In Clarissa, Richardson sets the tone for the story to follow with the first letter, which is from Miss Howe, Clarissa’s closest confidant, to Clarissa, and concerns the pernicious influence upon Clarissa’s family of Robert Lovelace, the man who becomes obsessed with marrying Clarissa to the point that he drugs and rapes her and arranges for her confinement in a brothel. Letter I of Volume I of Clarissa includes the following passage:

My mother, and all of us, like the rest of the world, talk of nobody but you on this occasion, and of the consequences which may follow from the resentments of a man of Mr. Lovelace's spirit; who, as he gives out, has been treated with high indignity by your uncles. My mother will have it, that you cannot now, with any decency, either see him, or correspond with him. She is a good deal prepossessed by your uncle Antony; who occasionally calls upon us, as you know; and, on this rencounter, has represented to her the crime which it would be in a sister to encourage a man who is to wade into her favour (this was his expression) through the blood of her brother.

The importance, and the function of the letters in Richardson’s novel lies in their composition and use as a narrative device. They allow the characters to share their innermost thoughts, and to convey matters of great substance without the need for dialogue.